1. Field of the Invention
The present invention relates to apparatus for decelerating projectiles in a fluid medium, and more specifically to a device for effectively decelerating projectiles of various weights and sizes with a single structure.
2. Description of the Prior Art
Projectile recovery devices are needed, particularly in the laboratory or test facility environment, for recovering test vehicles or projectiles by stopping them before they are damaged or otherwise rendered unusable.
Unlike actual at sea launches, in the laboratory these vehicles must be stopped within a reasonable distance. The rate at which the vehicle is decelerated must be on the same order of magnitude, or less than the acceleration the device experiences during launch. In fact, the peak deceleration should preferably be considerably less than the peak acceleration at launch. If deceleration levels are higher than acceleration at launch, possible damage to the vehicle cannot be ascribed directly to the launch phase and could be caused during the deceleration phase. As a result, discrepancies in collected data can arise due to the inability to ascribe them to one of these phases of the vehicle's flight path.
Elongated tubes or pipes that rely on fluid friction to slow the vehicle are known. Also, bumpers can be incorporated at the end of such pipe in case the vehicle does not stop in time. Another method of stopping vehicles is to provide a pipe of varying diameter along the path of travel of the vehicle. However, the pipe diameter profile is typically sized so as to achieve a predetermined velocity profile and deceleration through a known length of the pipe. The diameter profile is directly dictated by the distance within which the particular vehicle must be decelerated.
Vehicle recovery systems of this general type are shown in U.S. Pat. Nos. 3,940,981, 4,002,064 and 5,125,343.
The most recent of these, U.S. Pat. No. 5,125,343 relates to a projectile recovery system using an elongated pipe such that the projectile acts as a piston moving downstream in the water filled pipe. Ports are provided for radially releasing some of the fluid from the pipe, while fluid friction from the clearance provided between the pipe and the projectile acts upon the projectile to decelerate it. In the '064 patent, rifling is provided in the pipe to achieve substantially the same result as that provided for in the '343 patent. The '981 patent teaches the use of quick opening valves which alter the pressure in the pipe at different stations located in the axial direction of travel of the projectile.
The principal object of the present invention is to provide a single structure that is adapted to accommodate projectile type vehicles of different sizes and weights. The above mentioned prior art devices are intended to handle projectiles of only a predetermined size, diameter and weight.